It will build a new office on the corner of Ahtanhum Road and Longfibre Avenue.
The regional director says the new building will be more energy efficient and better fit the agency's needs.
"We looked at a couple other proposals that were in the downtown that were submitted in our bid request and unfortunately they were either more than we could afford or they weren't quite right for our business needs," said Tom Tebb Department of Ecology Central Director.
The department's lease in Yakima is up next June. Ecology hopes to break ground on the new building this fall.